254 



PROGRESS IN MICROSCOPY 



is focused on a virtually pin-point image on to the specimen. This 

 method is suitable for such arrangements as those shown, e.g. in 

 Figs. 10.5 and 10.6. 



3. THE OBJECT IS ILLUMINATED IN WHITE LIGHT 



Figure 10.11 shows the diagram of this arrangement. The specimen 

 P is illuminated by a source of light (not shown in Fig. 10.11) furnish- 

 ing a continuous spectrum. The objective O^ projects an enlarged 

 image of P on the slit F of the spectrograph. The spectrum is collected 



Fig. 10.11. Diagram of a basic system for microspectrophotometry in which the object 



is illuminated in white light. 



on the photographic plate at E. The investigated detail A' is con- 

 veniently set so that it overspreads only a portion of the slit F, e.g. the 

 lower part. The upper part is overspread by a vacant area of the 

 specimen serving as reference and, on said part, a rotatable and 

 adjustable sector is set which furnishes on the plate E a series of 

 spectra whose black levels provide a photometric scale for all wave- 

 lengths. As in the methods described in § 2, the photographic plate 

 may be substituted for physical receivers. 



